The present invention generally relates to a magnetic disk apparatus. More specifically, the present invention is directed to a seek control means for moving a magnetic head to a target position.
In a hard disk drives functioning as an external storage apparatus of a computer, a magnetic head is transported to a target track on a rotated magnetic disk so as to read/write data with respect to the target track.
Generally speaking, a magnetic head positioning control system contains a following control system, a seek control system, and a settling control system (refer to, for example, Japanese Laid-open Patent Application No. HEI-9-73618). In the following control system, a magnetic head is continuously followed to the same track in order to read/write data with respect to the same track. The seek control system moves the magnetic head up to a target track where data is present. The settling control system couples the seek control system to the following control system in the vicinity of the target track.
In the seek control system, when a move distance is longer than, or equal to a predetermined distance, there are some cases that a voltage applied to a voice coil motor “VCM” is saturated in order that a maximum acceleration capability of this voice coil motor VCM is derived during accelerating operation. In an actual system, since there is an upper limit velocity in move velocitys of a head, the head must be moved in uniform motion at a maximum velocity in such a case that a move velocity of the head is reached to the upper limit velocity.
With respect to such a seek control system, a velocity control system is employed. This velocity control system feeds back a deference between a target velocity, which is determined by remaining distance (a difference between a target track and a present position), and a head velocity, which are predicted from head position signals.
In this velocity control system, the VCM voltage during accelerating operation can be saturated and the movement at a constant velocity can be realized.
On the other hand, in a relatively short move distance, the VCM voltage is not saturated during the accelerating operation, and also, the move velocity does not exceed the upper limit of the move velocity, so that the Two Degree of Freedom control system is employed which uses the smooth acceleration waveform by the function of time.
This Two Degree of Freedom control system can suppress vibrations which are produced during the seek operation, and can use the position feedback system having the high error compression characteristic.
In the velocity control system for producing the target value based upon the remaining distance, since the jerk of the control input is large, the vibrations are readily produced in the mechanism system, and the error compression characteristic thereof is low, as compared with the position control system. As a result, undesired sound may occur in the seek operation, and vibrations are readily produced in the mechanism system during settling operation.
On the other hand, the Two Degree of Freedom control system by the function of time cannot avoid that when the VCM voltage saturation occurs, the performance thereof is deteriorated due to the wind-up phenomenon, and also cannot manage the limitation of the maximum velocity. As a result, this Two Degree of Freedom control system can be hardly applied to the seek system in which the head is moved over the long distance.
With respect to such a problem, in the patent publication 1, such a seek control system is disclosed in which the feedforward system corresponds to the VCM voltage saturation and the uniform velocity mode as the velocity control system, and the feedback system is employed as the position control system.
In Japanese Laid-open Patent Application No.HEI-9-73618, since the feedback control system is the position control system, the high disturbance compression characteristic may be expected. However, since the feedforward control system is equal to the velocity control system for producing the target value based upon the remaining distance, this feedforward control system can hardly suppress the mechanism system vibrations.
An object of the present invention is to provide a hard disk drives provided with a seek control means containing a seek control system capable of managing also a VCM voltage saturation and a uniform velocity mode during seek operation, which produces low vibrations.